1. Field of the Invention
The present invention relates to an oil seal which is disposed at the boundary portion between the inside and outside of a machine, for example, agricultural machinery, in order to prevent intrusion of external muddy watter, dust or other foreign matter into the machine and further prevent a lubricating oil, for example, in the machine from leaking to the outside.
2. Description of the Prior Art
A known oil seal of the type described above is constructed as follows: As shown in FIG. 1, a metal ring 102 of L-shaped cross-section is fitted at its outer peripheral portion to a machine housing 101. A seal lip 105 having a main lip 103 and a dust lip 104 is secured to the inner peripheral portion of the metal ring 102. The respective distal ends of the main lip 103 and the dust lip 104 are brought into slide contact with the outer peripheral surface of a rotating shaft 106 received in the housing 101. Thus, the main lip 103 serves to prevent a liquid, such as a lubricating oil, in the housing 101 from leaking to the outside. On the other hand, the dust lip 104, which is disposed on the side of the seal lip 105 which is closer to the atmosphere side, serves to prevent foreign matter, such as external water or dust in the air, from entering the inside of the housing 101. Moreover, grease is filled in a space 107 defined by the main lip 103, the dust lip 104 and the rotating shaft 106 so as to lubricate the area of slide contact between the main lip 103 and the dust lip 104 on one hand and the rotating shaft 106 on the other.
The above-described conventional oil seal, however, suffers the following problems: It is difficult to bring the inner peripheral edge of the dust lip 104 into close contact with the outer peripheral surface of the rotating shaft 106 over the entire circumference thereof owing to, for example, manufacturing errors. Accordingly, it is not possible to satisfactorily prevent intrusion of external dust or water. In addition, since the space 107 defined by the main lip 103, the dust lip 104 and the rotating shaft 106 has a relatively small volume, the grease filled in the space 107 inconveniently disappears within a short period of time, which causes the dust lip 104 to become worn quickly, resulting disadvantageously in a reduction in the life thereof.